1. Field of the Invention
The present invention relates to a stencil printer or similar printer and more particularly to a sheet feeding apparatus and a sheet discharging apparatus selectively connectable to a printer and capable of conveying paper sheets or similar recording media at a variable speed adaptive to a plurality of print speeds available with the printer.
2. Description of the Background Art
Conventional printers, including stencil printers, include a printer of the type allowing various kinds of peripheral units or apparatuses to be selectively connected thereto. Typical of peripheral units are a multi-tray sheet discharging apparatus configured to distribute paper sheets or similar recording media, which are prints carrying an image thereon each and sequentially driven out of a printer body, to a plurality of trays and a mass sheet feeding apparatus and a mass sheet discharging apparatus configured to feed and discharge, respectively, a great amount of paper sheets. Such peripheral units each are provided with a particular sheet feed speed or sheet discharge speed matching the respective property. Generally, the sheet feed speed and sheet discharge speed are selected to be adaptive to a plurality of print speeds available with a printer.
However, some peripheral units are not adaptive to higher print speeds required of modern printers, so that sheet jams ascribable to sheet feed errors or sheet discharge errors are apt to occur. Further, whether or not the print speed of the printer body is adequate cannot be determined unless a peripheral unit is connected to and operated with the printer body, forcing the operator of the printer to set the optimum print speed by hand.
For example, it is a common practice with a stencil printer to mount a first or body sheet feeding apparatus on the printer and connect a second or multi-tray sheet feeding apparatus (sheet bank) to the printer. In this configuration, the operator of the printer is allowed to select either one of the first and second sheet feeding apparatuses and a desired print speed on a control panel. Sheet feed speeds available with the first and second sheet feeding apparatuses are sometimes different from each other, e.g., the former and the latter are respectively a hundred and thirty paper sheets and a hundred and twenty paper sheets for a minute that correspond to the sixth and fifth print speeds, respectively.
Assume that the operator selects the sixth print speed of the printer, i.e., a hundred and thirty paper sheets for a minute on the control panel and then selects the second sheet feeding apparatus in accordance with the size of paper sheets to use. Then, the sheet feed speed of the second sheet feeding apparatus, which is a hundred and twenty paper sheets for a minute, is lower than the print speed, resulting in a sheet jam in the sheet feeding apparatus. Stated another way, the operator recognizes the mismatch of the sheet feed speed and print speed only after the sheet jam occurred in the sheet feeding apparatus and then replaces the sixth print speed with the fifth print speed. This not only requires the operator to perform troublesome jam processing, but also wastes time and paper sheets.
On the other hand, assume that the operator initially selects the fifth print speed matching the second or multi-tray sheet feeding apparatus in accordance with the sheet size to use, changes the second sheet feeding apparatus to the first sheet feeding apparatus before the start of printing, stacks paper sheets on the first sheet feeding apparatus, and then causes the printer to start operating. Then, the printer starts operating at the fifth print speed, i.e., a hundred and twenty paper sheets for a minute initially set. This brings about a problem that the sixth print speed, i.e., a hundred and thirty paper sheets for a minute matching the first sheet feeding apparatus is simply wasted. Although the operator, forgotten to reconfirm the print speed after changing the sheet feeding apparatus, may be responsible for such an occurrence, it is harsh to blame only the operator regarding the reconfirmation.
Japanese Patent No. 3,236,064 (corresponding U.S. Pat. No. 5,279,217) discloses a printer configured to control print speed to preselected one in matching relation to the type of a sheet discharging apparatus connected to the printer. While this printer, matching its print speed to the sheet discharging apparatus, successfully obviates sheet jams as far as the sheet discharge side is concerned, the print speed thus matched to the sheet discharging apparatus cannot be varied.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 6-199028 (corresponding U.S. Pat. No. 5,517,913), 6-247027 (corresponding U.S. Pat. No. 5,537,920), 9-11597 and 2004-167806